An Orion exploration vehicle approaches a near-Earth asteroid in this artist's conception. Such a mission would be carried out in 2021 under the White House's new plan for NASA exploration beyond Earth orbit.

NASA's accelerated vision for exploration calls for moving a near-Earth asteroid even nearer to Earth, sending out astronauts to bring back samples within a decade, and then shifting the focus to Mars, a senior Obama administration official told NBC News on Saturday.

The official said the mission would "accomplish the president's challenge of sending humans to visit an asteroid by 2025 in a more cost-effective and potentially quicker time frame than under other scenarios." The official spoke on condition of anonymity because there was no authorization to discuss the plan publicly.

The source said more than $100 million would be sought for the mission and other asteroid-related activities in its budget request for the coming fiscal year, which is due to be sent to Congress on Wednesday. That confirms comments made on Friday by Sen. Bill Nelson, D-Fla., a one-time spaceflier who is now chairman of the Senate Commerce Subcommittee on Science and Space. It also confirms a report about the mission that appeared last month in Aviation Week.

The asteroid retrieval mission is based on a scenario set out last year by a study group at the Keck Institute for Space Studies. NASA's revised scenario would launch a robotic probe toward a 500-ton, 7- to 10-meter-wide (25- to 33-foot-wide) asteroid in 2017 or so. The probe would capture the space rock in a bag in 2019, and then pull it to a stable orbit in the vicinity of the moon, using a next-generation solar electric propulsion system. That would reduce the travel time for asteroid-bound astronauts from a matter of months to just a few days.

The Keck study estimated the total mission cost at $2.6 billion — but the administration official said the price tag could be reduced to $1 billion, or roughly $100 million a year, if the mission took advantage of an already-planned test flight for NASA's heavy-lift Space Launch System rocket and Orion crew exploration vehicle. That flight would send astronauts around the moon and back in 2021.

"This mission would combine the best of NASA's asteroid identification, technology development, and human exploration efforts to capture and redirect a small asteroid to just beyond the moon to set up a human mission using existing resources and equipment, including the heavy-lift rocket and deep-space capsule that have been under development for several years," the official said in an email.

The 2014 budget would set aside $78 million for planning the asteroid retrieval mission, plus $27 million to accelerate NASA's efforts to detect and characterize potentially hazardous asteroids. The federal government currently spends $20 million annually on asteroid detection.

Meteor sparked actionThe official said the plan had been under discussion for months, but coalesced after February's meteor blast over Russia. The meteor's breakup injured more than 1,000 people and sparked a worldwide sensation. It also sparked a series of congressional hearings about threats from space, during which Republicans as well as Democrats hinted that they would support more funding to counter asteroid threats.

"This plan would help us prove we're smarter than the dinosaurs," said the official, referring to the asteroid that wiped out the dinosaurs and many other species 65 million years ago. An asteroid in the 7- to 10-meter range would be about half as wide as the one that broke up over Russia. That's far too small to pose any threat to Earth, even if the space rock was coming directly at our planet. But the captured asteroid could provide valuable insights for dealing with bigger ones in the future.

Initial preparations for the mission won't have to wait for a deal to end budget sequestration, or approval of the budget for the 2014 fiscal year. NASA would begin immediately to identify the asteroid for retrieval, and take advantage of existing efforts funded by the agency's science, technology and human exploration directorates. The most expensive element of the plan, the multibillion-dollar Orion/SLS launch system, is already being funded under the terms of an agreement with Congress.

Discussions with NASA's international and commercial partners will continue in the months and years ahead, the official said. The retrieved asteroid could conceivably become a target for other scientific missions or asteroid-mining operations. In the process, governments might have to address issues surrounding the ownership and exploitation of space resources.

"We're trying to force the question," the official said. "We're trying to push the envelope on this new frontier."

Questions raisedSome observers have already raised questions about the plan, based on the advance reports. Scott Pace, the director of George Washington University's Space Policy Institute, told The Associated Press that it was a bad idea on scientific as well as diplomatic grounds. It would be better for the United States to join forces with other countries to conduct a comprehensive survey of all potentially dangerous asteroids, Pace said.

Rick Tumlinson, chairman of an asteroid-mining venture called Deep Space Industries, said he was concerned that NASA's asteroid mission might interfere with private-sector efforts — and he called on NASA to rely on private enterprise wherever possible. The administration official assured NBC News that cooperation with commercial ventures as well as other groups such as the B612 Foundation was part of the plan.

The official noted that the mission would provide a relatively low-cost route to satisfying President Barack Obama's goal of sending astronauts to a near-Earth asteroid by 2025. The lessons learned during the mission could be applied to future missions aimed at diverting other asteroids — perhaps to head off a potential threat, or conduct further scientific study, or exploit the potentially valuable resources that asteroids contain.

After the asteroid mission, NASA would turn its attention to a farther-out destination: Mars. The Obama administration has called for astronauts to travel to the Red Planet and its moons by the mid-2030s, and that would be the next major target for space exploration. The administration official told NBC News that other concepts, such as sending astronauts back to the moon or creating a deep-space platform beyond the far side of the moon, are not on the agenda for the foreseeable future.